1 files changed, 72 insertions, 0 deletions
diff --git a/numpy/random/_examples/cffi/extending.py b/numpy/random/_examples/cffi/extending.py
new file mode 100644
index 000000000..732cbbb1d
--- /dev/null
+++ b/numpy/random/_examples/cffi/extending.py
@@ -0,0 +1,72 @@
+"""
+Use cffi to access the underlying C functions from distributions.h
+"""
+import os
+import numpy as np
+import cffi
+ffi = cffi.FFI()
+
+inc_dir = os.path.join(np.get_include(), 'numpy')
+
+# Basic numpy types
+ffi.cdef('''
+    typedef intptr_t npy_intp;
+    typedef unsigned char npy_bool;
+
+''')
+
+with open(os.path.join(inc_dir, 'random', 'bitgen.h')) as fid:
+    s = []
+    for line in fid:
+        # massage the include file
+        if line.strip().startswith('#'):
+            continue
+        s.append(line)
+    ffi.cdef('\n'.join(s))
+        
+with open(os.path.join(inc_dir, 'random', 'distributions.h')) as fid:
+    s = []
+    in_skip = 0
+    for line in fid:
+        # massage the include file
+        if line.strip().startswith('#'):
+            continue
+
+        # skip any inlined function definition
+        # which starts with 'static NPY_INLINE xxx(...) {'
+        # and ends with a closing '}'
+        if line.strip().startswith('static NPY_INLINE'):
+            in_skip += line.count('{')
+            continue
+        elif in_skip > 0:
+            in_skip += line.count('{')
+            in_skip -= line.count('}')
+            continue
+
+        # replace defines with their value or remove them
+        line = line.replace('DECLDIR', '')
+        line = line.replace('NPY_INLINE', '')
+        line = line.replace('RAND_INT_TYPE', 'int64_t')
+        s.append(line)
+    ffi.cdef('\n'.join(s))
+
+lib = ffi.dlopen(np.random._generator.__file__)
+
+# Compare the distributions.h random_standard_normal_fill to
+# Generator.standard_random
+bit_gen = np.random.PCG64()
+rng = np.random.Generator(bit_gen)
+state = bit_gen.state
+
+interface = rng.bit_generator.cffi
+n = 100
+vals_cffi = ffi.new('double[%d]' % n)
+lib.random_standard_normal_fill(interface.bit_generator, n, vals_cffi)
+
+# reset the state
+bit_gen.state = state
+
+vals = rng.standard_normal(n)
+
+for i in range(n):
+    assert vals[i] == vals_cffi[i]